The fundamental objective of this Program in Immunopathogenesis of Chronic Graft Rejection is to address "TA: Viral and Host Mechanisms" by understanding pathogenic processes underlying this common manifestation of chronic rejection in heart transplant recipients. The Program Project focuses on the contribution of human cytomegalovirus (HCMV) in conjunction with immunopathogenic and inflammatory modulation that develops in patients who progress to TA. The study involves a large, organized multi-level evaluation of 160 heart transplant recipients. Peripheral blood and endomyocardial biopsy specimens will be collected eight times over the first year and three times in successive years to follow immune, virologic and inflammatory indicators that will be correlated with TA. The first project in this program will focus on the contribution of the HCMV-specific CD4 and CD8 T cell memory/effector function during the reactivation from latent or the initiation of primary infection and the progression to TA. This project will also investigate the activation state of cells. An inverse correlation is expected between the risk of progression to TA and the frequency of functional HCMV-specific T cells. The second project of this program will focus on levels of HCMV DNA and the induction of viral gene expression in patients at risk of TA. Sensitive solution and in situ DNA amplification and hybridization approaches will be used to follow viral DNA and mRNA levels in the follow-up period. This project will investigate the role of virus encoded or -induced chemokine (UL146/vCXC-l) and chemokine receptor (US28) expression in progression of TA. The proinflammatory capacity of viral strains and the highly variable UL146 chemokine gene, from patients progressing to TA will be investigated. An increase in virological indicators is expected during progression to TA. The third project will determine the impact of the Nitric Oxide Synthase(NOS) pathway by focusing on two major changes that can be measured in patients: (i) increases in vascular superoxide anion (O2-), and (ii) increases in ADMA. This project will investigate how HCMV infection augments these abnormalities via cytokine induced alterations in oxidative stress and ADMA accumulation. An impact of HCMV on endothelial and inflammatory NOS pathways is expected during progression to TA. Importantly, all three projects will work in parallel in peripheral blood cells/plasma/serum as well as directly in endomyocardial biopsies at all sampling times. Such an intense longitudinal study should provide the best possible setting to uncover associations and identify the contribution of HCMV to TA. The mechanisms, prognostic value and points of therapeutic intervention-directed at HCMV, the immune response to HCMV, immune activation and immunopathogenic events and the role of NOS pathways will all potentially emerge as a result of these collaborative efforts.